Optical waveguide devices can be used as optical phase shifters and delay lines and can also be used to filter, modulate and switch optical signals. Mechanical and/or electrical contacts to optical waveguide devices are essential for many applications. Such contacts, however, can perturb the resonant modes of light being transmitted in the optical waveguide devices; and this can result in propagation losses of the light in these devices. In a microring resonator, the reduction of a quality factor, Q, in the microring resonator will limit the utility of the resonator for many applications including communications where a large resonator Q is needed for narrowband filtering, switching, or modulation. In other types of optical waveguide devices including interferometers, phase shifters and delay lines, propagation losses can also occur from electrically contacting an optical waveguide therein. What is needed is a way of making low-loss mechanical and electrical connections to optical waveguide devices which does not introduce any appreciable propagation loss.
The present invention provides a solution to these needs by providing optical waveguide devices in which mechanical and/or electrical contacts are made from inside of each optical ring resonator therein so that the Q of each ring resonator is preserved and so that the size of each ring resonator can be reduced to as small as 2-3 μm radius.
The present invention also provides a solution to electrically contacting waveguide devices which do not employ an optical ring resonator, by providing a waveguide bend (also termed a microbend) in an optical waveguide, with the waveguide bend varying adiabatically in width between a minimum value of the width and a maximum value thereof. By contacting the optical waveguide at a location near the maximum value of the width, the modes of light therein will not be substantially perturbed. This allows either an electrical heater or a semiconductor junction to be located inside the waveguide bend for use in varying an effective index of refraction of the optical waveguide and thereby changing an optical path length or phase delay of the light therein. This is useful, for example, to form a tunable interferometer (e.g. a Mach-Zehnder interferometer), or to form an optical delay line.
In an optical waveguide devices formed according to the present invention with a ring resonator, the optical waveguide used to form the ring resonator can similarly have a non-uniform width which adiabatically varies between a maximum value and a minimum value. By mechanically or electrically contacting the ring resonator from the inside thereof at a location near the maximum value of the width, the resonant modes of the light circulating in the optical waveguide ring are not substantially perturbed. This allows either an electrical heater or a semiconductor junction to be located inside the ring resonator for use in varying (i.e. tuning) a resonant frequency therein while maintaining a high resonator Q.
The optical waveguide devices of the present invention can be formed from silicon using conventional silicon integrated circuit (IC) processes. This allows one or more of the devices of the present invention to be co-located on a conventional silicon-on-insulator substrate together with integrated electronic circuitry to provide a capability for optical phase shifting, signal routing, switching, filtering and detection.
These and other advantages of the present invention will become evident to those skilled in the art.